Make stack trace annotation work

The code now unminifies all calls in the stack, including those outside
of app.js.

This requires the Python package sourcemap, recently added as a
dependency.

(imported from commit 550c73ad5bfe78a2c7169c11da0c95cbaac238d7)

zephyr/management/commands/explain_js_error.py

@@ -28,14 +28,14 @@ def get_full_paste():
         os.system('stty cooked echo')
 
 class Command(BaseCommand):
-    args = '<source map file>'
+    args = '<source map directory>'
     help = '''Add source locations to a stack backtrace generated by minified code.
 
 The currently checked out code should match the version that generated the error.'''
 
     def handle(self, *args, **options):
         if len(args) != 1:
-            raise CommandError('No source map file specified')
+            raise CommandError('No source map directory specified')
 
         source_map = SourceMap(args[0])